The KBH Vehicle Weight Efficiency Formula multiplies a vehicle's average track-width times its wheelbase-length to arrive at vehicle- platform-square-units. Then the formula divides the vehicle-weight by the vehicle-platform-square-units to arrive at a weight-per-square- unit index value. Finally, the formula uses the vehicle engine-power- per-vehicle-weight as a percentage and reduces the index value by the percentage to arrive at a final index value. The lower the final index value the greater the weight efficiency of the vehicle. Additionally, the final index value could be scaled to convenient output.
Here is a link to the KBH web page: